JPH0492873A - Porous ceramic body and production thereof - Google Patents

Abstract

PURPOSE:To improve air permeability, durability, chemical resistance and mechanical strength of a porous ceramic body by forming a kneaded material of inflammable powder grain, ceramic raw material powder, binder and liquid for kneading, drying the formed article and then burning the formed article in specific conditions. CONSTITUTION:100wt.% raw material consisting of 15-80wt.% inflammable powder grain (e.g. PVA), 20-75wt.% ceramic raw material powder (e.g. alumina) near to globe as much as possible and 3-50wt.% binder (e.g. kaolin based clay) is kneaded with 10-45wt.% liquid (e.g. water) for kneading and the kneaded material is formed and then dried to provide the formed article. Then the formed article is burned while giving temperature gradient along the direction of length or thickness or either part of the formed article is burned in a non- oxidizing atmosphere and other part thereof is burned in an oxidizing atmosphere to provide the porous ceramic body having two different porosities in one body and continuously changed in porosities of the boundary area.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to catalyst carriers, bioreactors, gas passing bodies and liquid passing bodies such as filter media, wicking evaporation devices, aroma devices, insecticides, and solid lubricants. , relates to a porous ceramic body used as a solid abrasive and a method for manufacturing the same.

[Conventional technology]

In recent years, porous ceramic bodies have been widely used especially in gas separation, ultrafiltration, microfiltration, bioreactors, wicking evaporation equipment, etc., and depending on the usage conditions, they have various properties such as heat resistance and chemical resistance. is required. In particular, the porosity, pore diameter, and pore distribution are extremely important physical properties for a porous ceramic body to fully exhibit its functions and maintain its functions for a long period of time.

However, conventionally, in this type of porous ceramic body, 1
The porosity, pore size, and pore distribution throughout the body were uniform.

Therefore, when trying to obtain ceramic bodies with different porosity and pore diameter as a single body, it is necessary to bond several types of ceramic bodies with different porosity and pore diameter with adhesive, or to Methods have been used, such as bonding and firing the molded bodies, or coating one ceramic body with the other ceramic material.

[Problem to be solved by the invention]

However, these ceramic bodies have problems with the mechanical strength of the bonded surface, the heat resistance and chemical resistance of the bonded part when used, and furthermore, the porosity and pore size change too rapidly. The application was not necessarily favorable as the requirements could not be met. In addition, when ceramic bodies with different porosity and pore diameter are bonded and sintered after heat degreasing or sintering, shrinkage etc. will not occur uniformly, so the The fluidity imparting agent etc. gasified and accumulated, causing cracks to occur, and furthermore, due to the imbalance of expansion and contraction, fatal defects such as dimensional instability of the finished product were likely to occur.

[Means to solve the problem]

As a result of intensive studies to solve the above problems, the inventors of the present invention found that when firing a molded article in which combustible powder and granules are mixed and kneaded,
When the molded body is fired by changing the temperature or oxidation conditions along the length direction or the thickness direction, the degree of burnout of the powder and granules differs, so that portions with different porosity exist in the body, Moreover, it has been discovered that a porous ceramic body in which the porosity of the boundary region continuously changes can be obtained, and the present invention has been achieved.

That is, the object of the present invention is to provide a porous ceramic body in which at least two portions with different porosity exist in one porous ceramic body, and the porosity of the boundary region changes continuously, and The purpose is to provide a manufacturing method.

Therefore, the object of the present invention is to mold a kneaded material containing flammable particles, ceramic raw material powder, a caking agent, and a mixing liquid, dry it, and then mold it along the length direction or thickness direction of the molded product. This can be easily achieved by firing with a temperature gradient, or by firing one in a non-oxidizing atmosphere and the other in an oxidizing atmosphere.

The present invention will be explained in detail below.

The raw material for the porous ceramic body of the present invention contains flammable powder and granules made of graphite, carbon, carbon precursors, etc. All of the flammable powder and granules are easily burnt out as carbon dioxide gas by burning. However, after being burnt off, pores having almost the same shape as the powder and granules are formed, and when the powder and granules are burned away as carbon dioxide gas, the pores are connected to each other to form continuous pores. Here, as organic substances and synthetic resins, polyvinyl alcohols, starches, and various CMCs that effectively act as adhesives are used.

Of course, gums such as gum arabic are also included in the combustible powder.

When powder particles as close to spherical as possible are used as these combustible powder particles, the pores of the resulting porous ceramic body become close to spherical, and various properties such as air permeability and durability are further improved.
This results in a preferred ceramic body. To obtain powders as close to spherical as possible, use powders that are initially approximately spherical, such as synthetic resin beads, or knead organic powders such as CMC1 starch with water and granulate them. There are methods such as using a raw material that has been pulverized by a method that yields spherical or approximately spherical powder particles. It is also effective to heat and harden the spherical granules of organic matter or to use them as a carbon precursor as a raw material.

By using these combustible powder particles whose particle size has been adjusted and adjusting the amount used, the porosity and pore diameter of the porous ceramic body to be produced can be easily adjusted, which is preferable.
As the powder, it is preferable to select a powder or granule whose particle size is slightly larger than the desired pore size, taking into account shrinkage during firing. By using the body, products with excellent properties such as breathability and durability can be obtained.

On the other hand, ceramic raw material powders include alumina, silica,
Any of the commonly used ceramic raw material powders can be used, such as zirconia, talc, mica, shirasu, perlite, seed stone, kaolin-based and montmorillonite-based clays, and powders made by granulating clays. In this case as well, in order to obtain a porous ceramic body with excellent air permeability and durability, it is desirable that the raw material powder be as close to spherical as possible.

When trying to obtain powder particles of alumina, silica, etc. that are more nearly spherical, it is necessary to use raw material powder obtained by grinding using a grinding method that produces approximately spherical particles, or to use talc, mica, etc. In the case of originally flat powder or clay, it is best to knead it with an organic binder to obtain the desired particle size, and then granulate it by firing or sintering. When a caking agent is used, it is possible to obtain a ceramic powder that foams during firing and is itself porous. There is also a method of using a ceramic raw material that expands in volume during sintering and forms a spherical shape, such as pearlite, shirasu, orite.

It is desirable to select a type of ceramic raw material powder that matches the properties of the intended ceramic body, and unless the clay is used without granulation, it should be selected according to the desired pore size. It is better to select a powder with a particle size slightly larger than the pore size, and furthermore, if you use a powder with as uniform a particle size as possible as the ceramic raw material powder, the pore size of the product ceramic body will be uniform. Instead, it becomes possible to suppress the phenomenon in which the fluidity imparting agent rapidly expands during firing and causes cranking.

The binders used as raw materials in the present invention include inorganic binders such as clay, aluminum phosphate, water glass, and basic aluminum chloride, rubbers such as talacant gum, gum arabic, and cypro rubber, CMC, starch PVA, and Although any organic binder such as various synthetic resins can be used, clay is preferred because it is easy to dry, cross-wire, mold, etc., and is easy to handle without damaging equipment. When using kaolin clay as a raw material, a porous ceramic body with a large specific surface area and particularly excellent adsorption performance can be produced.

On the other hand, when montmorillonite clay is used, it is possible to produce a porous ceramic body that has a relatively small specific surface area but is suitable for use in passing fluids such as filter media without adsorbing them. Although organic caking agents exhibit properties as caking agents, they also have properties as combustible powder particles that are burned away during firing and form continuous pores in the product, so they are not the main caking agents. Even when an inorganic binder such as clay is used as the binder, it is preferable to use these organic binders in combination. In particular, for the purpose of forming continuous pores, it is preferable to use CMC or various starches.

In this specification, clay has been described as a material contained in both ceramic raw material powder and caking agent, but in boat fishing, clays are usually treated as ceramic raw material powder and are hardened by firing to form a ceramic body. While it has the effect of imparting strength to the whole, it also has a sufficient effect as a caking agent, and when clay is used as a raw material in the present invention, it is not necessarily necessary to use other ceramic raw material powders or caking agents together. .

In the production of a ceramic body, a kneading liquid is used that is appropriately selected from water, alcohol, organic solvents, etc., depending on the properties of the raw materials used when kneading each raw material. The smaller the particle size of the raw material and the more organic raw materials used, the more crosstalk liquid needs to be added, but in the case of the present invention, if at least the crosstalk liquid that evaporates during firing is used, it will reduce the amount of crosstalk in the product. It is also effective in making the pores continuous. In addition, it is useful in the case of laminated molding of different types of kneaded materials, and the amount of addition is 10 to 10% in the kneaded material immediately before molding, in order to make it as if the same kneaded material during laminated molding with a desired porosity. 45
It is preferable to adjust the amount within a range of % by weight.

As mentioned above, when using ceramic raw material powder that is relatively close to spherical, or ceramic raw material powder that expands in volume during firing, the above-mentioned combustible powder such as graphite, carbon, carbon precursor, etc. Even if granules are not used, the gaps between the particles of the ceramic raw material powder form continuous pores, and a porous ceramic body exhibiting relatively good properties can be easily produced. In that case, the particle size, amount, combination with other materials, etc. of the ceramic raw material powder used are exactly the same as the method of the present invention, except that combustible powder is used. Specifically, for example, powdered material obtained by crushing industrially obtained silica lumps with a grinder, or raw materials such as shirasu balloons, pearlite, and staghorn, which are classified into the following ranges, are mixed with clay, water, etc. , and if necessary, knead with a small amount of organic binder, shape (extrusion, molding, lamination, slurry casting, etc.), and after drying,
A porous ceramic body that is fired in a furnace with a temperature gradient or in a non-oxidizing state on one side is a ceramic body that has different porosity, pore diameter, etc. in the length direction or thickness direction. It exhibits good properties in terms of air permeability, liquid permeability, durability, etc.

In the present invention, in addition to the above-mentioned raw materials, other materials may be used in combination, including materials normally used for manufacturing ceramic bodies, such as fluidity imparting agents. Specifically, in the raw material kneading process, A porous ceramic body with better air permeability can be produced by incorporating carbonates such as soda carbonate, soda bicarbonate, and calcium carbonate into the material and foaming them during firing. 5-30 in raw materials excluding
It is preferable to set it as wt%, Furthermore, calcium hydroxide,
By incorporating hydroxides such as magnesium hydroxide and aluminum hydroxide into the raw material kneading material and decomposing it during firing to release water and leave pores, a porous ceramic body with excellent air permeability is created, similar to the above. can be produced, and the content of hydroxide is preferably 5 to 35% in the raw materials excluding the crosstalk liquid.

The present invention involves adding a mixing liquid to each of the above-mentioned materials, kneading them, and molding them by layer molding, slurry casting, die molding, extrusion molding, etc., in which several types of kneaded materials are layered according to the purpose. The molded product is dried, and a temperature gradient is created in the length direction or thickness direction of the molded product, or it is fired in a non-oxidizing atmosphere in either the length direction or the thickness direction. Although the mixing ratio of combustible powder and granules is not particularly limited, the mixing ratio of
80 t%, ceramic raw material powder 20-75 wt%, caking agent 3-50 t% (total amount of raw materials outside the ice field is 100 wt%)
It is preferable to determine the mixing ratio of each raw material in accordance with the characteristics desired for the product, including the porosity, within the range of 1.5% (t%).

As mentioned above, cases where the ceramic raw material powder also serves as a caking agent and cases where combustible powder and granules also serve as a caking agent are within the scope of the present invention, and in that case, the mixing ratio is the same as each of the above. It is best to set it appropriately by referring to the raw material ratio.

The most distinctive feature of the present invention is that the ceramic body has portions with different porosity in the length direction or thickness direction, and the porosity of the boundary area changes continuously. However, in order to achieve this purpose, when mixing the above powders and granules, it is also possible to mix two or more types of combustible powders with different burnout temperatures in relation to the firing method. It is valid.

In the firing process, the temperature is gradually raised to a temperature at which the combustible powder is burnt out on the high temperature side or in an oxidizing atmosphere, and then, more preferably, the heating is temporarily stopped, and the forming process is carried out on the high temperature side or in an oxidizing atmosphere. When the temperature is raised again after the powder and granules in the body have been sufficiently burned and burned out, it is possible to prevent the occurrence of cracks and produce products with better air permeability and durability. Firing after the combustible powder is burned out may be performed entirely in a reducing atmosphere, or the temperature may be raised to a temperature at which the ceramic raw material is partially sintered.

Furthermore, ceramic bodies generally have a pale yellow color, but they can be colored freely by adding various high-temperature pigments, ceramic pigments, metals such as chromium, cobalt, nickel, iron, copper, or metal compounds, as appropriate. It is also possible to do so.

In order to manufacture a ceramic body with a black color, in addition to using pigments as described above, in order to prevent combustible powders such as graphite, carbon, and carbon precursors from being completely burnt out, the ceramic body must first be relatively heated in an oxidizing atmosphere. Firing at a low temperature for a short time, then under a non-oxidizing atmosphere,
The porous ceramic body is fired at a high temperature, or is treated with various synthetic resins such as phenolic resin, furan resin, etc.
After impregnating liquid paraffin wax, molasses, and various organic substances in a solution, it is best to re-fire by adjusting the temperature, time, and/or atmosphere so as not to completely burn out the carbon content. In either case, graphite or The carbonaceous material remains in the pores, and a blackish ceramic body can be easily produced.

EXAMPLES The present invention will be explained in detail below using Examples, but the present invention is not limited to these Examples unless the gist of the invention is exceeded.

〔Example〕

(Example 1) 30 parts by weight of approximately spherical polyethylene beads whose particle size was adjusted to 20 to 40 μm (hereinafter "parts" refer to parts by weight),
35 parts of mica powder whose particle size has been adjusted to 43 to 74 μm, 30 parts of kaolin clay, 5 parts of CMC manufactured by Daicel, and 1 part of polyethylene glycol #400 manufactured by NOF Corporation are mixed with 23 parts of water, and the outer diameter is 10 mm. Formed into a cylindrical shape with a length of 100 mm, dried at 80°C for 24 hours, buried 50 mm in the length direction in graphite powder, and left uncovered until carbonization of the polyethylene beads was completed at 450°C for 15 hours. As a result of increasing the temperature over time and then sintering it to 1200℃, the side embedded in graphite powder had an average pore diameter of 20 μm and a porosity of 61%.
On the open side, a porous ceramic body having an average pore diameter of 25 μm and a porosity of 67% and having portions with different porosity within one body was obtained.

(Example 2) 35 parts of approximately spherical acrylic resin beads whose particle size was adjusted to 20 to 40 μm, Ijichi Winlight (Shirasu Balloon)
30 parts, 30 parts of kaolin clay, 5 parts of CMC, 1 part of polyethylene glycol #400 manufactured by Nihon Yushi Co., Ltd., and 25 parts of water were added and kneaded.Thickness: 30W+, length: 100m, width: 100m
After drying at 80°C for 48 hours, 15 m thick plate was embedded in graphite powder, and the other 15 m plate was sintered in the same manner as in Example 1 without a lid. As a result, the side embedded in graphite powder had an average pore diameter of 22 μm and a porosity of 5.
9%, and the open side had a pore diameter of 28 μm and a porosity of 70%, yielding a porous ceramic body having portions with different porosity in one body.

(Example 3) 23 parts of water was added to 34 parts of raw coke powder whose particle size was adjusted to 43 to 74 μm, 34 parts of mica powder whose particle size was also adjusted to 43 to 74 μm, 26 parts of kaolin clay, 5 parts of CMC, and 1 part of polyethylene glycol. The mixture was kneaded and formed into a plate shape with a thickness of 30 m, a length of 100 ++ s, and a width of 100 m. After drying at 80°C for 42 hours, it was sintered in the same manner as in Example 2. After impregnating with oil at °C, the temperature was raised to 1020 °C for 10 hours under a reducing gas-solid atmosphere, and the temperature was raised to 1020 °C for 2 hours at 1020 °C.
After holding for 10 hours, it was slowly cooled to room temperature. As a result, one had an average pore diameter of 48 μm and a porosity of 55%, and the other had an average pore diameter of 55 μm and a porosity of 62%. A quality ceramic body was obtained.

(Example 4) 32 parts of graphite powder whose particle size was adjusted to 61 to 104 μm, 43 parts
22 parts of water was added to 41 parts of mica powder adjusted to ~74 μm, 20 parts of kaolin clay, 5 parts of CMC, 1 part of nickel oxide, and 1 part of polyethylene glycol, and kneaded to form a diameter of 7.5 μm.
It was extruded into a rod shape with a length of 100 mins, dried at 80°C for 24 hours, and then embedded in silica powder with 50 mins lengthwise.
The temperature was raised to 600°C for 15 hours, 6 hours from 600°C to 850°C, and 5 hours from 850°C to 1050°C.
After holding for 8 hours, the mixture was slowly cooled to room temperature. One has an average pore diameter of 62 μm and a porosity of 56%, and the other has an average pore diameter of 70 μm.
A black porous ceramic body having a porosity of 65% and having portions with different porosity in one body was obtained.

[Effects of the Invention] According to the porous ceramic body and the manufacturing method thereof of the present invention, parts with different porosity exist in one body, and the pores in the boundary area are continuous, so that the porous ceramic body has good air permeability. Since no adhesive method is used, porous ceramic bodies with excellent durability, chemical resistance, and mechanical strength can be easily produced without cranking, deformation, etc. It is used in various applications such as liquid passing, gas passing, and filtration media, which require delicate adjustment of the temperature, as well as durability, chemical resistance, and strength, and provide great industrial benefits. be.

Claims (2)

[Claims] (1) A porous ceramic body characterized in that at least two parts having different porosity exist in one porous ceramic body, and the porosity of the boundary area changes continuously. (2) A kneaded product containing combustible powder, ceramic raw material powder, caking agent, and kneading liquid is molded and dried, and a temperature gradient is created along the length or thickness direction of the molded product. 1. A method for producing a porous ceramic body, the method comprising firing one porous ceramic body in a non-oxidizing atmosphere and the other in an oxidizing atmosphere.